1. Field of the Invention
The present invention relates to modular components for prosthetic joints. More particularly, the present invention relates to a method for selecting modular neck components for prosthetic hip joints.
2. Description of the Related Art
Orthopedic prosthetic implants are commonly used to replace some or all of a patient's hip joint in order to restore the use of the hip joint, or to increase the use of the hip joint, following deterioration due to aging or illness, or injury due to trauma. In a hip replacement, or hip arthroplasty procedure, a femoral component is used to replace a portion of the patient's femur, including the femoral neck and head. The femoral component is typically a hip stem, which includes a stem portion positioned within the prepared femoral canal of the patient's femur and secured via bone cement, or by a press-fit followed by bony ingrowth of the surrounding tissue into a porous coating of the stem portion. The hip stem also includes a neck portion adapted to receive a prosthetic femoral head. The femoral head may be received within a prosthetic acetabular component, such as an acetabular cup received within the prepared recess of the patient's acetabulum.
Orthopedic implants for hip replacement may include modular hip joint components. For example, the hip stem and the neck portion with femoral head are formed as separate components. Prior to an operation, a surgeon chooses a hip stem and a neck portion based on patient anatomy, body image scans, and/or other patient-specific data. However, during surgery, the surgeon may discover that a different hip stem or a different neck portion is desired to provide more optimum results. Modular hip joint components allow the surgeon to choose a different hip stem or neck portion depending on the specific application and needs of the patient and surgeon. Typically, the surgeon will only change the neck portion because the hip stem is usually implanted first, and removal of the hip stem from the femoral intramedullary canal is generally undesirable. Thus, the neck portion is usually the component that is most often changed intraoperatively. The surgeon may be provided with a number of different neck portions to accommodate various patient anatomies.
In one known system, for example, the surgeon chooses from a plurality of options to replace an existing neck portion with an alternative neck portion to provide the best outcome for the patient. The surgeon's choices rely on the location of the center of rotation of the femoral head component of the implant. Referring to FIG. 1, an image of a proximal femur 20 is shown and includes femoral head 22, greater trochanter 24, lesser trochanter 26, femoral neck 28, and a portion of femoral shaft 27. FIG. 1 illustrates a portion 30 of a template used in the known system. The template may also include images of the femur, similar to those described below with reference to FIGS. 3 and 4. Portion 30 of the template may be placed over the image of proximal femur 20 acquired preoperatively to plan the optimum location of the center of the femoral head of the implant. Portion 30 of the template may include a plurality of reference points 32, 34 arranged in a generally fan-shaped arrangement. Each reference point represents the center of rotation for the femoral head component of the implant. Typically, reference points 32, 34 may be based on a spherical or cylindrical coordinate system. If the surgeon desires an intra-operative change which differs from the preoperatively chosen modular neck portion, the surgeon must simultaneously evaluate at least three variables based on the center of rotation of the femoral head of the implant, and may need to consult various tables to evaluate these variables based on physical characteristics of the patient in order to choose an optimal implant.